The proposed Storage Factory Project mainly consists of the development of a new gas storage pool by leaching caverns within existing bedded salt formations in Tioga County, Pennsylvania for the purpose of storing and cycling high pressure natural gas to be used in conjunction with DTI’s other storage facilities. A new compressor station will be constructed adjacent to the leaching operations at the storage pool for gas storage injection/withdrawal purposes. In order to utilize the new capacity and deliverability created from the pool, DTI is also proposing on-system enhancements to other existing facilities in Pennsylvania.
The initial phase of the project is designed to place 11.2 MMDT of new storage capacity in-service in January 2014. This will consist of 2.5 Bcf of working gas in the initial salt cavern and 8.4 Bcf of new storage capacity from on-system enhancements and utilization of DTI’s integrated storage system. ()
The major components of the project are listed below:
Salt Cavern Gas Storage Development ()
Salt cavern development for hydrocarbon (gas) storage is an engineering methodology that has been in existence for several decades with a well-documented process and procedural history. The first criteria for successful development of a salt cavern requires suitable salt formations that may be bedded (layered) or domal (massive) in nature. Some of the critical criteria specifications include an adequate thickness of a salt deposit at a feasible depth in the ground, a suitable source of fresh water, a brine disposal plan, and logistical infrastructure to support the development and desired future use of the cavern. The Storage Factory Project meets all of these critical development criteria for successful cavern development.
The resulting process and procedure to develop a salt cavern in Tioga, Pennsylvania will initially require the simultaneous development of two salt caverns to be able to place one cavern in service. This development process is commonly known in the industry as “cascading”, where freshwater is introduced into the first cavern at high rates and then cycled as a non-fully saturated brine stream to the second cavern. Cycling the brine through the second cavern allows the stream to become fully saturated and economically feasible for salt processing and production. During the initial cavern development stages the water contact with the salt walls is limited and the leaching process results in non-saturated weak brine incapable of efficient salt production. As the first cavern’s size increases due to the ongoing leaching process, the subsequent water contact time with the salt walls increases as does the resulting saturation level of the brine stream. Hence the second cavern in the cascading development process is leached at a very minimal rate and is only partially developed when the first cavern is completely ready for service. In a multi-cavern design, the process and timeline is repeated for the development of additional salt caverns.
The Storage Factory Project will be developed in phases, and will depend on future market conditions. The initial phase for which pre-filing is requested involves the leaching of two salt caverns and placing the first cavern in service by 2014. While only one cavern will be placed in service in the initial phase, the simultaneous leaching of two caverns, or cascading, is required to fully saturate the brine from the first cavern for processing. At this time, DTI is requesting authorization only for the initial phase.
Each of the new storage caverns will be developed thru a single casing string cemented to surface and a casing shoe set approximately 150’ into the salt formation (anticipated in preliminary design to be approximately 4,860’ from the surface). All proposed cavern well-heads will be outside the active limits of DTI’s existing Tioga Storage Pool. Leaching will be controlled within each cavern in attempts to limit the cavern wall development so as to not encroach on the active limits of the Tioga Storage Pool. The preliminary design contemplates approximately 900’ to 1,000’ of vertical separation between the Tioga Storage Pool Oriskany formation (average depth of 4,000’) and the top of the salt cavern, which is anticipated at a depth of approximately 4,960’ from the surface. The total vertical height (roof to floor) of each cavern is anticipated to be approximately 1,300’, however, the eventual cavern floor will be considerably shallower given the significant amount of insoluables which will accumulate in the floor as the cavern is leached.
A leaching/pumping facility will be constructed as part of this project for the salt cavern solution mining. A raw water intake structure and approximately 1.25 miles of 6-inch water transfer piping will be utilized to transport fresh water from an existing water reservoir to leach the caverns. The storage caverns will tie into DTI’s adjacent interstate gas transmission system through approximately one mile of 30-inch storage tie-over pipeline.
The first cavern, when completed, will have an anticipated working gas storage capacity of approximately 2.5 Bcf and a total capacity of 4.4 Bcf. The preliminary design contemplates a maximum pressure gradient of 0.80 psi/ft and minimum cavern pressure gradient of 0.25 psi/ft. This is in contrast to the previous caverns proposed to be located within the active limits of the Tioga Storage Pool certificated by the Commission in N.E. Hub Partners, 83 FERC 61,043 ¶(1998), rehearing order, 90 FERC ¶61,142 (2001) (N.E. Hub Project), which proposed a maximum gradient of 0.9 psi/ft. and a minimum gradient of 0.15 psi/ft. The preliminary cavern design anticipates an average cavern diameter of approximately 200’. Once leaching is complete, DTI will conduct geological/sonar surveys to determine actual capacities and pressures, which will be filed with the Commission once the final data is collected and analyzed.
Future development of up to six more salt storage caverns is planned. However, that development is dependent upon market conditions and future regulatory approvals. Following completion of the initial phase, future caverns could be developed at the rate of approximately one new cavern every two years and will require system modifications to accommodate the incremental storage deliverability. Future cavern development, if it occurs, will be proposed in separate certificate applications or amendments.
Compressor Station ()
A new compressor station, with 4,735 hp, will be constructed adjacent to the leaching operations at the storage pool for gas storage injection/withdrawal purposes. This will also include the construction of associated gas processing facilities.
Brine Processing Facility ()
In the Gulf Coast region, of the United States, brine is often disposed of by re-injecting the stream into porous geologic formations back into the ground. The geology indicative to the Tioga, Pennsylvania region is not capable of supporting an adequate brine well re-injection process; hence the brine will be processed into salt commodity products. In order to do this, a brine processing facility will be constructed on a 38-acre site approximately one mile from the Town of Tioga, Pennsylvania. The brine processing facility will receive the saturated brine from the cavern leaching and convert the brine into salt commodity products. The facility will consist of a closed system evaporative process with little environmental impact. Water effluent will be piped back into the leaching operation by utilizing approximately 4.6 miles each of 10-inch and 8-inch brine transfer pipelines between the caverns and the brine processing facility. The processed salt products will be shipped via existing and adjacent rail and truck infrastructure.
Transmission Facilities, On-System Enhancements, and System Utilization
() ()
An additional 8.4 Bcf of new storage capacity will be derived from on-system enhancements and integration of the deliverability resulting from the new salt storage cavern capability with DTI’s existing system. Approximately 4.0 Bcf of the 8.4 Bcf will be developed from redefining base gas levels at DTI’s Sabinsville Storage Pool. To minimize gas velocities and pressure drop at low inventory levels, limited storage pool trunk lines will be replaced in DTI’s Sabinsville Storage Pool, as necessary. Proposed modifications to transmission related facilities include additional compression at DTI’s existing Ardell Station (approximately 4,000 HP) in Elk County, Pennsylvania, and approximately 7.5 miles of new 30” pipeline looping within an existing right-of-way in Clinton County, Pennsylvania, south of DTI’s Leidy and Finnefrock compressor stations. The remaining 4.4 Bcf will be derived from a portion of the previously-certificated, unsubscribed inventory of DTI’s integrated storage system capacity that was reserved by DTI for operational purposes, as approved by the Commission in a previous rate settlement docket.
|
